1. Field of the Invention
This invention relates to a receiver apparatus suitable for receiving, for example, a satellite broadcast and so on.
2. Description of the Prior Art
There has been known a satellite broadcast tuner (hereinafter referred to as "the BS tuner") which, for example, utilizes an AGC voltage of a tuner unit to calculate a received level and display the calculated received level on the screen of a television receiver connected thereto (or integrated therewith).
Since especially the BS tuner requires that a BS antenna be strictly set in an appropriate direction for receiving satisfactory images, it is quite useful to display a received level on the screen of a television receiver as a guide for determining an optimal setting direction of the antenna.
The received level calculated by the BS tuner is not a simple BS-IF level of a received channel but a value, for example, corresponding to a received C/N which is calculated by simultaneously measuring a received noise level at a predetermined frequency. This example will be described with reference to FIG. 1.
In that case, an IF level (carrier level) is calculated from an AGC voltage at an arbitrary channel (for example, BS channel 11) and a received level or a noise level at a frequency out of the received frequency band of the satellite broadcast channels (1st-15th channels), for example, a frequency corresponding to a channel 16.5 is similarly measured from the AGC voltage. The received level L.sub.CN is calculated, for example, by the following equation: ##EQU1## where K represents a correction coefficient, C.sub.f(x) a received level (carrier level) measured when it is received at a frequency of a channel x, and N.sub.f(16.5) a received level (noise level) measured when it is received at a frequency corresponding to the channel 16.5.
Measured values of the AGC voltages at the respective channels in a certain receiving condition present higher values as the channels are in a higher frequency region, for example, as indicated by solid lines illustrated in FIG. 1. This phenomenon is caused by the frequency characteristics of a BS converter, a BS cable, a bandpass filter used in a tuner unit, the AGC voltage and so on.
However, since the received levels of the respective channels derived by the prior art are calculated on the basis of a noise level (indicated by one-dot chain lines in FIG. 1) measured at a frequency outside the received frequency band, for example, at a frequency corresponding to the channel 16.5, the received levels of the respective channels are calculated as values corresponding to l (l1-l15) indicated by broken line arrows in FIG. 1.
That is, even if the angle and receiving condition of the antenna are identical for all the channels, a large error may be produced in the received level L.sub.CN calculated for certain channels, which results in confusing the user.